Time relay refers to a relay whose output circuit needs a specified accurate time to jump (or contact action) after the input action signal is added (or removed). It is an electrical component used in low voltage or low current circuits to connect or disconnect high voltage and high current circuits.
Time relay is a very important component in electrical control system. In many control systems, time relay is needed to realize time delay control. Time relay is an automatic control electrical appliance that uses electromagnetic principle or mechanical action principle to delay contact closure or disconnection. It is characterized in that there is a time delay between the signal of the attraction coil and the contact action. Time relay is generally used for motor starting process control as a function of time.
The main function of the time relay is as an executive device of simple program control. When it receives the start signal, it starts timing. After the timing, its working contact is opened or closed, so as to promote the subsequent circuit work. Generally speaking, the time delay performance of time relay can be adjusted within the design range, which is convenient to adjust its time delay. I'm afraid that one time relay alone can't start the delayed closing. Close it for a period of time and then open it to realize the delayed closing and then delayed opening, but generally speaking, it can be completed by configuring a certain number of time relays and intermediate relays.
With the development of electronic technology, electronic time relay has become the mainstream product of time relay. The electronic intelligent digital display time relay with large-scale integrated circuit technology has many working modes, which can not only realize long time delay, but also have high delay precision, small volume, convenient adjustment and long service life, making the control system more simple and reliable.
When selecting a time relay, pay attention to the current type and voltage level of its coil (or power supply), and select the delay mode, contact form, delay accuracy and installation mode according to the control requirements.
1、 Classification by working principle
According to different working principles, time relay can be divided into air damping time relay, electric time relay, electromagnetic time relay, electronic time relay, etc.
(1) The air damping time relay uses the damping principle of air passing through the small hole to obtain the time delay. Its structure is composed of electromagnetic system, time delay mechanism and contact. The electromagnetic mechanism is double port direct acting type, the contact system is microswitch, and the time-delay mechanism adopts airbag damper.
(2) Electronic time relay
The principle of electronic time relay is that the capacitor voltage in RC circuit cannot jump, but can only change gradually according to the exponential law, that is, the resistance characteristic can obtain time delay.
Features: wide delay range, up to 3600 s, high accuracy, generally about 5%, small size, impact resistance, convenient adjustment.
(3) Motor time relay motor time relay uses micro synchronous motor to drive reduction gear train to obtain time delay.
Features: the delay range is wide, up to 72 hours, and the delay accuracy can reach 1%. At the same time, the delay value is not affected by voltage fluctuations and ambient temperature changes.
The delay range and accuracy of motor time relay are unmatched by other time relays. Its disadvantages are complex structure, large volume, short service life, high price and accuracy affected by power frequency.
(4) Electromagnetic time relay. Electromagnetic time relay uses the principle of slow attenuation of magnetic flux after the power failure of electromagnetic coil to delay the release of armature of magnetic system and obtain the principle of contact delay action. It is characterized by large contact capacity, so the control capacity is large, but the delay time range is small and the accuracy is slightly poor. It is mainly used for the control of DC circuits.
2、 Classification by delay mode
According to different time-delay methods, time relays can be divided into power on time-delay type and power-off time-delay type.
(1) The power on delay relay starts to delay immediately after obtaining the input signal, and its executive part only outputs the signal to operate the control circuit after the delay is completed; When the input signal disappears, the relay immediately returns to the state before operation.
(2) The power-off delay relay is just the opposite. When the input signal is obtained, the execution part immediately has an output signal; However, after the input signal disappears, the relay needs a certain time delay to return to the state before action.